It has become known in recent years that the coefficient of restitution of a golf ball can be increased in a metallic hollow golf club head by using a titanium alloy or the like for an impact surface that impacts a golf ball, and in addition, by making the thickness of a face member that forms the impact surface thinner, or by making portions of a joining edge, where the face member is joined to other members such as a crown member and a sole member, partially thinner.
JP 10-155943 A discloses a hollow golf club head in which a thin portion is provided in an inner circumferential edge of a golf ball impact surface. Elastic deformation of the impact surface during golf ball impacts is thus promoted, thus increasing the restitution coefficient of the struck golf ball which results in an increase of the carry distance of the golf ball.
However, if the face member is made thinner in its entirety or partially, the rigidity of the face member itself decreases, and the mechanical strength with respect to an impact force during golf ball impacts decreases. Accordingly, there is a limit to how thin the face member can be made. A problem therefore exists in that the coefficient of restitution of a struck golf ball cannot be increased further by the above-described method of making the face member thinner in its entirety or partially.